Re: [PATCH v8 15/15] x86: EFI stub DRTM launch support for Secure Launch

Ard Biesheuvel
2024-02-15T09:01:17Z

On Wed, 14 Feb 2024 at 23:32, Ross Philipson <ross.philipson@oracle.com> wrote:
>
> This support allows the DRTM launch to be initiated after an EFI stub
> launch of the Linux kernel is done. This is accomplished by providing
> a handler to jump to when a Secure Launch is in progress. This has to be
> called after the EFI stub does Exit Boot Services.
>
> Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
> ---
> drivers/firmware/efi/libstub/x86-stub.c | 55 +++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> index 0d510c9a06a4..4df2cf539194 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -9,6 +9,7 @@
> #include <linux/efi.h>
> #include <linux/pci.h>
> #include <linux/stddef.h>
> +#include <linux/slr_table.h>
>
> #include <asm/efi.h>
> #include <asm/e820/types.h>
> @@ -810,6 +811,57 @@ static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry)
> return EFI_SUCCESS;
> }
>
> +static void efi_secure_launch(struct boot_params *boot_params)
> +{
> + struct slr_entry_uefi_config *uefi_config;
> + struct slr_uefi_cfg_entry *uefi_entry;
> + struct slr_entry_dl_info *dlinfo;
> + efi_guid_t guid = SLR_TABLE_GUID;
> + struct slr_table *slrt;
> + u64 memmap_hi;
> + void *table;
> + u8 buf[64] = {0};
> +

If you add a flex array to slr_entry_uefi_config as I suggested in
response to the other patch, we could simplify this substantially

static struct slr_entry_uefi_config cfg = {
.hdr.tag = SLR_ENTRY_UEFI_CONFIG,
.hdr.size = sizeof(cfg),
.revision = SLR_UEFI_CONFIG_REVISION,
.nr_entries = 1,
.entries[0] = {
.pcr = 18,
.evt_info = "Measured UEFI memory map",
},
};

cfg.entries[0].cfg = boot_params->efi_info.efi_memmap |
(u64)boot_params->efi_info.efi_memmap_hi << 32;
cfg.entries[0].size = boot_params->efi_info.efi_memmap_size;

> + table = get_efi_config_table(guid);
> +
> + /*
> + * The presence of this table indicated a Secure Launch
> + * is being requested.
> + */
> + if (!table)
> + return;
> +
> + slrt = (struct slr_table *)table;
> +
> + if (slrt->magic != SLR_TABLE_MAGIC)
> + return;
> +

slrt = (struct slr_table *)get_efi_config_table(guid);
if (!slrt || slrt->magic != SLR_TABLE_MAGIC)
return;

> + /* Add config information to measure the UEFI memory map */
> + uefi_config = (struct slr_entry_uefi_config *)buf;
> + uefi_config->hdr.tag = SLR_ENTRY_UEFI_CONFIG;
> + uefi_config->hdr.size = sizeof(*uefi_config) + sizeof(*uefi_entry);
> + uefi_config->revision = SLR_UEFI_CONFIG_REVISION;
> + uefi_config->nr_entries = 1;
> + uefi_entry = (struct slr_uefi_cfg_entry *)(buf + sizeof(*uefi_config));
> + uefi_entry->pcr = 18;
> + uefi_entry->cfg = boot_params->efi_info.efi_memmap;
> + memmap_hi = boot_params->efi_info.efi_memmap_hi;
> + uefi_entry->cfg |= memmap_hi << 32;
> + uefi_entry->size = boot_params->efi_info.efi_memmap_size;
> + memcpy(&uefi_entry->evt_info[0], "Measured UEFI memory map",
> + strlen("Measured UEFI memory map"));
> +

Drop all of this

> + if (slr_add_entry(slrt, (struct slr_entry_hdr *)uefi_config))

if (slr_add_entry(slrt, &uefi_config.hdr))

> + return;
> +
> + /* Jump through DL stub to initiate Secure Launch */
> + dlinfo = (struct slr_entry_dl_info *)
> + slr_next_entry_by_tag(slrt, NULL, SLR_ENTRY_DL_INFO);
> +
> + asm volatile ("jmp *%%rax"
> + : : "a" (dlinfo->dl_handler), "D" (&dlinfo->bl_context));

Fix the prototype and just do

dlinfo->dl_handler(&dlinfo->bl_context);
unreachable();

So in summary, this becomes

static void efi_secure_launch(struct boot_params *boot_params)
{
static struct slr_entry_uefi_config cfg = {
.hdr.tag = SLR_ENTRY_UEFI_CONFIG,
.hdr.size = sizeof(cfg),
.revision = SLR_UEFI_CONFIG_REVISION,
.nr_entries = 1,
.entries[0] = {
.pcr = 18,
.evt_info = "Measured UEFI memory map",
},
};
struct slr_entry_dl_info *dlinfo;
efi_guid_t guid = SLR_TABLE_GUID;
struct slr_table *slrt;

/*
* The presence of this table indicated a Secure Launch
* is being requested.
*/
slrt = (struct slr_table *)get_efi_config_table(guid);
if (!slrt || slrt->magic != SLR_TABLE_MAGIC)
return;

cfg.entries[0].cfg = boot_params->efi_info.efi_memmap |
(u64)boot_params->efi_info.efi_memmap_hi << 32;
cfg.entries[0].size = boot_params->efi_info.efi_memmap_size;

if (slr_add_entry(slrt, &cfg.hdr))
return;

/* Jump through DL stub to initiate Secure Launch */
dlinfo = (struct slr_entry_dl_info *)
slr_next_entry_by_tag(slrt, NULL, SLR_ENTRY_DL_INFO);

dlinfo->dl_handler(&dlinfo->bl_context);

unreachable();
}

> +}
> +
> static void __noreturn enter_kernel(unsigned long kernel_addr,
> struct boot_params *boot_params)
> {
> @@ -934,6 +986,9 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
> goto fail;
> }
>
> + /* If a Secure Launch is in progress, this never returns */

if (IS_ENABLED(CONFIG_SECURE_LAUNCH))

> + efi_secure_launch(boot_params);
> +
> /*
> * Call the SEV init code while still running with the firmware's
> * GDT/IDT, so #VC exceptions will be handled by EFI.
> --
> 2.39.3
>